When I was in grad school, I heard from some of his students how, every so often, he would get the itch to do some programming (I think this would have been Alice, their 3D virtual world). The students asked him to mark where he started and where he ended in the source code, so they could go fix things afterward, all in good humor.
Randy also claimed to be the person who started the trend in SIGGRAPH papers of including a giant splash image at the top of the first page, as part of his Aladdin paper. Here's a copy of the paper. http://ivizlab.sfu.ca/arya/Papers/ACM/SIGGRAPH-96/Storytelli...
He was also notorious for how he started the first day of class of Programming User Interfaces (a class for non-programmers about prototyping user interfaces). He would bring in a VCR and a sledgehammer. He would talk about how bad user interfaces would make people so angry, they would want to smash things. He would then proceed to smash the VCR into bits. I heard that some students would come to the first day just to see him do this. (I took over that course several years ago, and no, I definitely don't do that!)
Randy was a really great person, I still miss him.